<html>
 <head>
  <link href="./leetcode-problem.css" rel="stylesheet" type="text/css">
 </head>
 <body>
  <div class="question_difficulty">
   难度：Hard
  </div>
  <div>
   <h1 class="question_title">
    759. Set Intersection Size At Least Two
   </h1>
   <p>
    An integer interval
    <code>
     [a, b]
    </code>
    (for integers
    <code>
     a &lt; b
    </code>
    ) is a set of all consecutive integers from
    <code>
     a
    </code>
    to
    <code>
     b
    </code>
    , including
    <code>
     a
    </code>
    and
    <code>
     b
    </code>
    .
   </p>
   <p>
    Find the minimum size of a set S such that for every integer interval A in
    <code>
     intervals
    </code>
    , the intersection of S with A has size at least 2.
   </p>
   <p>
    <b>
     Example 1:
    </b>
    <br>
   </p>
   <pre>
<b>Input:</b> intervals = [[1, 3], [1, 4], [2, 5], [3, 5]]
<b>Output:</b> 3
<b>Explanation:</b>
Consider the set S = {2, 3, 4}.  For each interval, there are at least 2 elements from S in the interval.
Also, there isn't a smaller size set that fulfills the above condition.
Thus, we output the size of this set, which is 3.
</pre>
   <p>
    <b>
     Example 2:
    </b>
    <br>
   </p>
   <pre>
<b>Input:</b> intervals = [[1, 2], [2, 3], [2, 4], [4, 5]]
<b>Output:</b> 5
<b>Explanation:</b>
An example of a minimum sized set is {1, 2, 3, 4, 5}.
</pre>
   <p>
    <b>
     Note:
    </b>
    <br>
   </p>
   <ol>
    <li>
     <code>
      intervals
     </code>
     will have length in range
     <code>
      [1, 3000]
     </code>
     .
    </li>
    <li>
     <code>
      intervals[i]
     </code>
     will have length
     <code>
      2
     </code>
     , representing some integer interval.
    </li>
    <li>
     <code>
      intervals[i][j]
     </code>
     will be an integer in
     <code>
      [0, 10^8]
     </code>
     .
    </li>
   </ol>
  </div>
  <div>
   <h1 class="question_title">
    759.  设置交集大小至少为2
   </h1>
   <p>
    一个整数区间&nbsp;
    <code>
     [a, b]
    </code>
    &nbsp;&nbsp;(&nbsp;
    <code>
     a &lt; b
    </code>
    &nbsp;) 代表着从&nbsp;
    <code>
     a
    </code>
    &nbsp;到&nbsp;
    <code>
     b
    </code>
    &nbsp;的所有连续整数，包括&nbsp;
    <code>
     a
    </code>
    &nbsp;和&nbsp;
    <code>
     b
    </code>
    。
   </p>
   <p>
    给你一组整数区间
    <code>
     intervals
    </code>
    ，请找到一个最小的集合 S，使得 S 里的元素与区间
    <code>
     intervals
    </code>
    中的每一个整数区间都至少有2个元素相交。
   </p>
   <p>
    输出这个最小集合S的大小。
   </p>
   <p>
    <strong>
     示例 1:
    </strong>
   </p>
   <pre>
<strong>输入:</strong> intervals = [[1, 3], [1, 4], [2, 5], [3, 5]]
<strong>输出:</strong> 3
<strong>解释:</strong>
考虑集合 S = {2, 3, 4}. S与intervals中的四个区间都有至少2个相交的元素。
且这是S最小的情况，故我们输出3。
</pre>
   <p>
    <strong>
     示例 2:
    </strong>
   </p>
   <pre>
<strong>输入:</strong> intervals = [[1, 2], [2, 3], [2, 4], [4, 5]]
<strong>输出:</strong> 5
<strong>解释:</strong>
最小的集合S = {1, 2, 3, 4, 5}.
</pre>
   <p>
    <strong>
     注意:
    </strong>
   </p>
   <ol>
    <li>
     <code>
      intervals
     </code>
     &nbsp;的长度范围为
     <code>
      [1, 3000]
     </code>
     。
    </li>
    <li>
     <code>
      intervals[i]
     </code>
     &nbsp;长度为&nbsp;
     <code>
      2
     </code>
     ，分别代表左、右边界。
    </li>
    <li>
     <code>
      intervals[i][j]
     </code>
     的值是&nbsp;
     <code>
      [0, 10^8]
     </code>
     范围内的整数。
    </li>
   </ol>
  </div>
 </body>
</html>